Airborne 12.09.16

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Airborne 12.09.16

Ulysses Has Been Active Over 17 Years

After more than 17 years of
pioneering solar science, a joint NASA and European Space Agency
mission to study the sun will end on or about July 1.

The Ulysses spacecraft has endured for almost four times its
expected lifespan. However, the spacecraft will soon cease
operations because of a decline in power produced by its onboard
generators. Ulysses has forever changed the way scientists view the
sun and its effect on the surrounding space. Mission results and
the science legacy it leaves behind were reviewed Thursday at a
media briefing at European Space Agency Headquarters in Paris.

"The main objective of Ulysses was to study, from every angle,
the heliosphere, which is the vast bubble in space carved out by
the solar wind," said Ed Smith, Ulysses project scientist at NASA's
Jet Propulsion Laboratory, Pasadena, CA. "Over its long life,
Ulysses redefined our knowledge of the heliosphere and went on to
answer questions about our solar neighborhood we did not know to
ask."

Ulysses ends its career after revealing that the magnetic field
emanating from the sun's poles is much weaker than previously
observed. This could mean the upcoming solar maximum period will be
less intense than in recent history.

"Over almost two decades of science observations by Ulysses, we
have learned a lot more than we expected about our star and the way
it interacts with the space surrounding it," said Richard Marsden,
Ulysses project scientist and mission manager for the European
Space Agency (ESA). "Solar missions have appeared in recent years,
but Ulysses is still unique today. Its special point of view over
the sun's poles never has been covered by any other mission."

The spacecraft and its suite of 10 instruments had to be highly
sensitive, yet robust enough to withstand some of the most extreme
conditions in the solar system, including intense radiation while
passing by the giant planet Jupiter's north pole. The encounter
occurred while injecting the mission into its orbit over the sun's
poles.

"Ulysses has been a challenging mission since launch," said Ed
Massey, Ulysses project manager at JPL. "Its success required the
cooperation and intellect of engineers and scientists from around
the world."

Ulysses was the first mission to survey the environment in space
above and below the poles of the sun in the four dimensions of
space and time. It showed the sun's magnetic field is carried into
the solar system in a more complicated manner than previously
believed. Particles expelled by the sun from low latitudes can
climb to high latitudes and vice versa, sometimes unexpectedly
finding their way out to the planets. Ulysses also studied dust
flowing into our solar system from deep space, and showed it was 30
times more abundant than astronomers suspected. In addition, the
spacecraft detected helium atoms from deep space and confirmed the
universe does not contain enough matter to eventually halt its
expansion.

Ulysses collected and transmitted
science data to Earth during its 8.6 billion kilometer journey (5.4
billion miles). As the power supply weakened during the years,
engineers devised methods to conserve energy. The power has
dwindled to the point where thruster fuel soon will freeze in the
spacecraft's pipelines.

"When the last bits of data finally arrive, it surely will be
tough to say goodbye," said Nigel Angold, ESA's Ulysses mission
operations manager. "But any sadness I might feel will pale in
comparison to the pride of working on such a magnificent mission.
Although operations will be ending, scientific discoveries from
Ulysses data will continue for years to come."

Ulysses was launched aboard space shuttle Discovery on October
6, 1990. From Earth orbit, it was propelled toward Jupiter by
solid-fuel rocket motors. Ulysses passed Jupiter on February 8,
1992. The giant planet's gravity then bent the spacecraft's flight
path downward and away from the ecliptic plane to place the
spacecraft in a final orbit around the sun that would take it past
our star's north and south poles.

The spacecraft was provided by ESA. NASA provided the launch
vehicle and upper stage boosters. The US Department of Energy
supplied a radioisotope thermoelectric generator to provide power
to the spacecraft. Science instruments were provided by both US and
European investigators. The spacecraft is operated from JPL by a
joint NASA/ESA team.